Name

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    SIP_EVAL

Purpose

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    Compute distorted coordinates given SIP (simple imaging polynomial)
    coefficients.

Explanation

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    See http://fits.gsfc.nasa.gov/registry/sip.html for the SIP convention
     
    The coefficients are passed via common block. This is because this
    routine is called by the intrinisc BROYDEN() function in AD2XY, and
    common blocks are the only way to pass parameters to the user supplied
    function in BROYDEN().

Calling Sequence

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    res = SIP_EVAL(xy)

Inputs

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    xy - 2 elements vector giving the undistorted X,Y position

Outputs

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    res - 2 element vector giving the distorted position

Common Blocks

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      common broyden_coeff,xcoeff,ycoeff
      XCOEFF, YCOEFF are both nxn arrays giving the SIP coefficient for an
      n x n polynomial.

Revision History

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    Written W. Landsman Dec 2013